Added functionality to find highest priority safebrowsing result.

Comments

Added functionality to find highest priority safebrowsing result.
Rather than looking at the final redirect in the chain during safebrowsing
activation throttle result notification, the result with the highest priority is
now selected when making an activation decision. The notification of results
handle remains the same , and will be addressed in a later CL.
Change-Id: I639f78d5a3ae05a263a38c85e8a2f8b20b6d0b5d
Reviewed-on: https://chromium-review.googlesource.com/1058087
Commit-Queue: Eric Robinson <ericrobinson@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562966}